1. Field of the Invention
This invention relates to the field of rare earth-iron magnets.
Instruments using magnets have been widely used for rotary instruments such as motors and peripheral terminal devices of computers. As a rare earth-iron magnet has the highest maximum energy product of all available magnets on the market, it is easy to upgrade and miniaturize instruments using such magnets.
2. Description of the Prior Art
Before this invention, surface finishing technology such as aluminium-chromating, epoxy electrodeposition painting and nickel electrodeposition plating has been used to coat magnet surfaces because corrosion resistance is improved by coating the surface of the magnets with a protection layer for anti-corrosion of the rare earth-iron magnet.
The magnetic characteristics deteriorate, however, because a surface layer of the magnet is damaged by the prior art surface treatment technology. This problem appears particularly in small-sized magnets having a large specific surface. For example, a small-sized rare earth magnet having a volume of 1.times.10.sup.-3 cm.sup.3 for a watch is improved in corrosion resistance by aluminium-chromating, but it is inferior by one and one-half times in coercive force and by one third in maximum energy product in comparison with a similar rare earth magnet not having such a surface treatment. Accordingly, such as surface-finished magnet is not suitable for practical use.